The present invention relates to impact-resistant, transparent molding compositions based on polyvinyl chloride or on copolymers comprising at least about 80% by weight of vinyl chloride units.
It is known to improve the impact resistance of polyvinyl chloride by polymerizing vinyl chloride in the presence of an elastomer or by blending polyvinyl chloride with elastomer proportions. The resultant products are generally opaque.
Molding compositions of modified polyvinyl chloride having both impact resistance and a certain transparency have, however, also been described in the literature. Thus, DAS No. 2,013,020 describes transparent graft copolymers. In their manufacture, first of all a monomer blend of styrene or .alpha.-methylstyrene is graft-polymerized, in the presnce of comonomers having crosslinking effect and in the presence of acrylic and methacrylic acid nitrile or of acrylic and methacrylic acid esters, onto a butyl or 2-ethylhexyl acrylate polymer. Subsequently, polymerization of the vinyl chloride in suspension is carried out in the presence of the thus-produced graft polymer. Apart from the fact that the aforedescribed mode of operation for producing the rubber-elastic phase is expensive due to the plurality of steps and components, the notched impact resistance values demonstrated in the examples are comparatively low.
Transparent, impact-resistant polyvinyl chloride molding compositions have also been disclosed in German Patent No. 2,621,522. These molding compositions consist of three components, namely a vinyl chloride homo- or copolymer, a graft copolymer wherein methyl methacrylate and styrene are grafted on a butadiene rubber, and finally a copolymer of .alpha.-methylstyrene, methyl methacrylate, acrylonitrile, and optionally a further, copolymerizable monomer. On the one hand, this involves an expensive multistage process whose sequence of addition of the numerous components is disclosed as extraordinarily critical, even during the preparation of the elastomer proportion; on the other hand, a large number of components is employed; and, finally, the resultant molding compositions are not weatherable on account of the butadiene proportion (cf. DAS No. 2,013,020, column 1, lines 60 et seq.).
This disadvantage of lack of weatherability is eliminated in molding compositions wherein chlorinated polyethylene is added to raise the impact resistance of polyvinyl chloride, as described, for example, in German Pat. No. 2,456,278. Here, there is the drawback of the narrow limits for the chlorine content (38-42%), which can be maintained only with difficulty in performing the process; additionally, only low impact resistance values can be attained. Thus, for example, with the addition of 10% by weight of the special chlorinated polyethylene, impact resistances of only 7-8 kJ/m.sup.2 are produced.